Bicomponent elastomeric netting

ABSTRACT

The invention is an extruded bicomponent elastomeric netting having unidirectional elasticity. Such a netting product is a non-woven article employing a non-elastic material such as polypropylene ( 10 ) in the machine direction strands and an elastic material such as a styrenic block copolymer ( 12 ) in the cross machine direction strands. The reverse arrangement, a product with “reverse strand distribution”, is also possible.

BACKGROUND OF THE INVENTION

1. Field of The Invention

This invention relates to plastic netting, and more particularly to anextruded bicomponent elastomeric netting having unidirectionalelasticity, that is in either the machine direction or the transversedirection.

2. Description of the Related Art

For purposes of the present invention, the terms “cross machinedirection” and “transverse direction” are synonymous and sometimessimply referred to as “TD”, as are the terms “longitudinal direction”and “machine direction”, sometimes simply referred to as “MD”. However,the term “transverse” is sometimes also used to refer to strands whichextend in a direction opposite to that of strands previously referredto. The meaning will be clear from the context in any particularinstance. Current production elastomeric roll goods, such as scrims,sheets, films, foams, nettings, nonwovens, fibers, threads and the likeare basically isotropic, exhibiting essentially the same properties inall directions of their two dimensional plane. However, in manyapplications, elastomeric properties are desired in only one direction,while elastomeric properties in the other direction are unnecessary oreven detrimental to product functionality. Although numerous patentsexist describing netting, woven and non-woven fabrics, meshes and chainnets with bicomponent materials or unidirectional elasticity or netlikearticles, they do not provide any suggestion to modify the prior artsuch as is done in the present invention with respect to extrudedplastic net. Existing technology does not include an extrudedbicomponent elastomeric netting with unidirectional elasticity which maybe manufactured more economically than most conventional elastomericnetting on the market.

Nets, wovens and nonwoven reinforcements made of more than one materialare disclosed in U.S. Pat. No. 4,636,419 to Madsen, U.S. Pat. No.4,241,123 to Shih, and U.S. Pat. No. 4,460,633 to Kobayashi et al. Inaddition, a netting die fed by two separate polymer streams is disclosedin U.S. Pat. No. 3,791,784 to Arechavaleta.

U.S. Pat. No. 4,636,419 issued to Madsen et al on Jan. 13, 1987discloses a “Net and Method of Producing Same” which employs acombination of side by side extrusion streams, transversal embossment,and splitting to produce netting composed of a regular array oflongitudinal ribbon-formed continuous polymer filaments and a regulararray of transverse stems or strands of a different polymer matter. Itis disclosed that the use of two different polymer substances in twodirections affords netting of interesting and unusual properties (col.2, Ins 12-25 and 30-31). In Example One, the cross machine componentcomprises Nylon 6 and the machine direction component comprisespolypropylene (col. 11, Ins. 13-31). It is disclosed that elastomericnetting may be prepared by the method of this patent, and preferredmaterials as well as a suitable application for such netting isdisclosed (col. 9, In. 67 through col. 10, In. 7). Unidirectionalelasticity in net as-extruded is neither disclosed nor suggested.

U.S. Pat. No. 4,241,123 issued to Shih on Dec. 23, 1980 disclosesnon-woven netting wherein a first group of melting monofilaments are dieextruded and a second group of monofilaments or a yam is crossed,pressed, and welded to form a welded plastic netting (col. 3, Ins.8-12). Unidirectional elasticity is not disclosed.

U.S. Pat. No. 4,460,633 issued to Kobayashi et al on Jul. 17, 1984discloses a nonwoven reinforcement for resinous composites made ofbundles of non-twist or soft twist yams as warps on both sides ofbundles of non-twist or soft twist yams as wefts, warps and wefts beingbonded by an adhesive agent impregnated into the wefts. This inventiondiffers from the present invention in that it does not suggestunidirectional elasticity, having flexure no different from that of awoven fabric.

U.S. Pat. No. 4,980,227 issued to Sekiguchi et al on Dec. 25, 1990discloses a stiff, netlike sheet of heat bonded five layer and threelayer polyolefin yams which exhibits retention of its sheet-like shapedue to its stiffness. Although heat bonding of polyolefin materials ismentioned, neither an extruded net nor the use of another material toproduce unidirectional elasticity is disclosed or suggested.

U.S. Pat. No. 3,791,784 to Arechavaleta discloses an extrusion die fedby two separate polymer streams. Although Arechavaleta suggests that twodifferent materials may be extruded, it is not suggested that the die beused to produce a resulting netting structure which will possess goodstrand to strand bond, uniform transverse direction strand spacing, or ahigh transverse direction packing density, i.e. transverse directionstrandcount, nor is a net having unidirectional elasticity suggested. Inparticular it is not suggested that netting strands made of twobasically incompatible resin groups, such as polyolefins and styrenicblock copolymers, can provide a good bond with the associated desirableproperties. Differences in polymer compatibility, rheology, processingmelt history, melt temperatures and the like contribute to theexpectation of a poor strand to strand bond as compared to a situationin which one polymer component is used for the two melt streams.

Fabrics, meshes, chain nets, and support materials with elasticproperties are disclosed in U.S. Pat. No. 4,107,371 issued to Dean, U.S.Pat. No. 4,673,015 issued to Andreasson, U.S. Pat. No. 4,728,565 issuedto Fontana, U.S. Pat. No. 4,469,739 issued to Gretzinger, and U.S. Pat.No. 4,351,872 issued to Brosseau et al. These products are expensive toproduce, and are significantly different from a netting product.

U.S. Pat. No. 4,107,371 issued to Dean on Aug. 15, 1978 discloses afabric woven of plastic-coated yam and polymer strands that isrelatively stiff in one direction and relatively flexible in the otherdirection. This differs from the present invention in that it does notdisclose, teach or suggest making an extruded net from two differentpolymers.

U.S. Pat. No. 4,351,872 issued to Brosseau et al on Sep. 28, 1982discloses a unidirectional stretch mesh laminate used in an orthopaedictraction hamess. A commercially available DuPont unidirectional stretchmesh is discussed at col. 3, Ins. 12-18 as a component of the invention.No patent was found disclosing said mesh.

U.S. Pat. No. 4,469,739 issued to Gretzinger on Sep. 4, 1984 disclosesan oriented woven furniture support material made in part from anelastomer monofilament and in part from synthetic or natural yarn.Unlike the extruded bicomponent elastomeric netting of the presentinvention, this material is woven, and is not completely plastic incomposition.

U.S. Pat. No. 4,673,015 issued to Andreasson on Jun. 16, 1987 disclosesa chain net which may include links of elastically deformable material.is suggested that although warp and weft strands are usually made oflinks of similarly elastic material, the weft strands may alternativelybe made of other material (col. 2, Ins. 49-64). Although unidirectionalelasticity is suggested, this patent does not disclose an extruded net.

U.S. Pat. No. 4,728,565 issued to Fontana on Mar. 1, 1988discloses anelastic support member for supporting stuffing of furniture piecescomprising an elastic net or belt formed of a net or honeycomb fabric ora woven fabric comprised of rubber threads arranged in at least one ofthe transverse and longitudinal directions. This patent is animprovement of Italian Patent No. 955,134. Although the appearance ofrubber threads in at least one direction suggests unidirectionalelasticity, this patent neither discloses nor suggests an extruded netas in the presently disclosed invention.

The art described in this section is not intended to constitute anadmission that any patent, publication or other information referred toherein is “prior art” with respect to this invention, unlessspecifically designated as such. In addition, this section should not beconstrued to mean that a search has been made or that no other pertinentinformation as defined in 37 C.F.R. §1.56(a) exists.

SUMMARY OF THE INVENTION

The present invention is an extruded bicomponent elastomeric nettinghaving unidirectional elasticity. It is economical to produce. Thebicomponent netting of the present invention may be produced by anextrusion die fed by two separate polymer streams. Such a netting is anon-woven employing a relatively non-elastic strand material in onedirection and a relatively elastic transverse strand material in theopposite direction. Any combination of resins with an elastomeric resinblend may be used, as long as the two types of resin strands arecompatible from processing and rheological standpoints. For example thestrands of the two resin streams should show good joint bond strength.The net may comprise preferably a non-elastic material such as apolyolefin in the machine direction and an elastic material in the crossmachine direction. A product with reverse strand distribution may alsobe produced, with the elastic material in the machine direction and thenon-elastic material in the cross machine direction. It was unexpectedlyfound that polyolefins and styrenic blok copolymers, two basicallyincompatible polymers, possess good bond strength. For the purposes ofthis invention, that combination represents a preferred embodiment ofthe invention. That preferred embodiment of the invention employs anelastic material of a styrenic block copolymer resin such as iscommercially available under the Kraton® brand from Shell Oil Company,Houston, Tex. or the Vector brand which is available from DexcoPolymers, a Dow/Exxon partnership, of Plaquemine, La. The non-elasticstrands are preferably in the machine direction in this preferredembodiment and may be oriented. Of course, the opposite arrangement ofstrands may be used according to this invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the netting of the present invention.

FIG. 2 is a the netting of FIG. 1 shown with the elastic strandsstretched.

FIG. 3 is a cross sectional view taken through the vertical axis of anextrusion die for making the netting of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

While this invention may be embodied in many different forms, there areshown in the drawings and described in detail herein specific preferredembodiments of the invention. The present disclosure is anexemplification of the principles of the invention and is not intendedto limit the invention to the particular embodiments illustrated.

Referring now to FIG. 1, The bicomponent elastomeric netting shown isextruded and may consist of strands of a relatively non-elastic material10 extending in one direction and strands 12 of a relatively elasticmaterial extending in a crosswise or transverse direction. The strandsare extruded polymeric elongate members which cross and intersect duringextrusion to form the net-like structure. In one preferred embodiment,the non-elastic material is polypropylene and the elastic material isthe commercially available Kraton® D grade class resin such as D-1122 orD-2104 from Shell Oil Company, Houston, Tex.

However, in its broad context, the non-elastic strand material may beany extrudable material such as the various nylons, polyesters,polyethylenes including HDPE and copolymers of such resins, thepolyolefins being preferred, polypropylene being especially preferred.

For the elastic strand material, in addition to the Kraton D grade classof styrene butadiene styrene (SBS) resins such as those aforementioned,the Vector brand extrusion grade resins such as Vector 6240D (SBS),6101D styrene isoprene styrene (SIS) and 6201D (SBS) are also preferred.Suitably the elastic strand material is a blend of SBS and SIS resins.Preferred blends are in the range of 50-70 parts SIS to 30-50 parts SBS.

Additional resins such as processing aid resins and slip agents may beadded to the elastic strand material in small amounts, such as about5-30 parts, to improve processability and to enhance physical propertiesof the elastic strand material. Improvement in processability is forexample evidenced by the ability to draw down strands of the mixture.Physical properties enhanced include improved melt strength, and elasticproperties such as stress relaxation, set and creep. These processingaid resins include isotatic polypropylene, polyethylene, amorphouspolypropylene, polybutylene, ethylene/vinyl acetate copolymer,ethylene/ethyl acrylate copolymer, ethylene/methyl acrylate copolymer,ethylene/methyl acetate copolymer, polystyrene and the like. Preferredresins are polystyrene, polyethylene, polybutylene, polypropylene,ethlene vinyl acetate (EVA) and ethylene methyl acetate (EMA), and themost preferred resin is polystyrene. The relative parts ratios may vary.

Depending on the elastomeric blend used, a slip additive may also beadded in an effective amount to prevent blocking, which occurs when thestrands of net become tacky and stick to themselves as well as the webhandling equipment. Examples of such slip additives are modified fattyacid esters or fatty acid amides.

The most preferred elastic strand material is a blend of SIS/SBS as setforth below:

60 parts SIS 40 parts SBS 25 parts Processing Aid Resins

Referring now to FIG. 3, an extrusion die 14 is shown for forming thebicomponent netting product. The machine direction strands (MD) 10 arethe non-elastic strands in this embodiment. In the most preferredembodiment, they are made of polypropylene, which is supplied to the dieunder pressure and which is discharged continuously from cavity 16through a plurality of openings (not shown) to form the MD strands. Theopenings do not appear in the cross section shown in FIG. 3. Thetransverse direction strands (TD) 12 are formed of a relatively elasticstyrenic block copolymer, such as a styrene-butadiene polymer. In themost preferred embodiment, an SIS/SBS blend is used. The elastomer issupplied to the die under pressure and intermittently discharged throughslit 18 shown partially open in FIG. 3 which is opened and closed by thereciprocating movement of piston 20. When piston 20 is moved to openslit 18 the elastomer flows out to form transverse TD strands 12 in theform of a closed ring intersecting with all of the MD strands. Thenetting is extruded in the form of a cylinder or tube, which is then cutlengthwise and flattened to form a continuous sheet. The non-elasticstrands (MD in this embodiment) may optionally be oriented in a secondprocessing step.

Since polyolefins and styrenic block copolymers, in combination apreferred embodiment, are two basically incompatible polymer groups, itwas unexpected that the bond strength of netting strands made from thesetwo materials would be well bonded at the joints. It is not obvious thatnetting strands made of two basically incompatible resin groups, such aspolyolefins and styrenic block copolymers, can provide a good bond withthe associated desirable properties. Differences in polymercompatibility, rheology, processing melt history, melt temperatures andthe like contribute to the expectation of a poor strand to strand bondas compared to a situation in which one polymer component is used forthe two melt streams.

A high bond strength is particularly required if the extrudedbicomponent netting is oriented in a second processing step. In thisprocess step, high forces are transferred and distributed through thenetting joint to and from netting strands in all directions. Without agood strand to strand bond at the joint, the product will fail. Theresulting product can consequently be made with uniform transversedirection strand spacing, high transverse direction strandcount, and isboth uniaxially and biaxially orientable and extensible.

Advantages of the bicomponent elastomeric net of the present inventionover all-elastomeric netting are many. For instance, the product may bedesigned with one set of properties in one direction, and another set ofproperties in the opposite direction. Specifically, high yield strengthand dimensional stability is designed by using a nonelastic polymer suchas polypropylene in one direction, while elastomeric properties areensured by the use of an elastomer such as Kraton® in the oppositedirection. The polypropylene/Kraton® combination also improves webhandling and processing of an elastomeric product for the nettingproducer, the converter and the end user. Further, overall product costmay be reduced by using expensive elastomeric resins only where neededand inexpensive resins elsewhere, and by increasing product yield orproduct area per resin mass through orientation of the nonelastic,polypropylene segments. Similarly, elastomeric product width may beincreased through orientation of the non-elastomeric segments.

This completes the description of the preferred and alternateembodiments of the invention. Those skilled in the art may recognizeother equivalents to the specific embodiment described herein whichequivalents are intended to be encompassed by the claims attachedhereto.

What is claimed is:
 1. A bicomponent elastomeric extruded netting havingunidirectional elasticity, said bicomponent elastomeric extruded nettingcomprising extruded strands consisting essentially of a relativelyinelastic resin component and transverse extruded strands consistingessentially of a relatively elastic resin component, wherein theinelastic strands are of a polyolefin resin.
 2. The netting of claim 1wherein the strands of the polyolefin resin extend in the machinedirection and the strands of the elastic resin extend in the transversedirection.
 3. The netting of claim 1 wherein the polyolefin ispolypropylene.
 4. The netting of claim 1 wherein the elastic resinfurther includes a processing aid resin selected from the groupconsisting of isotatic polypropylene, polyethylene, amorphouspolypropylene, polybutylene, ethylene/vinyl acetate copolymer,ethylene/ethyl acrylate copolymer, ethylene/methyl acrylate copolymer,ethylene/methyl acetate copolymer, polystyrene and mixtures thereof. 5.The netting of claim 4 wherein the elastic resin includes about 5-30parts of the processing aid resin.
 6. The netting of claim 5 wherein theparts are about
 25. 7. The netting of claim 4 wherein the elastic resinincludes about 5-30 parts of polystyrene.
 8. The netting of claim 4wherein the elastic resin includes an amount of a slip agent.
 9. Abicomponent elastomeric extruded netting having unidirectionalelasticity, said bicomponent elastomeric extruded netting comprisingextruded strands consisting essentially of a relatively inelastic resincomponent and transverse extruded strands consisting essentially of arelatively elastic resin component, wherein the elastic strands are of astyrenic block copolymer composition, and wherein the elastic resin is astyrene-isoprene-styrene resin.
 10. A bicomponent elastomeric extrudednetting having unidirectional elasticity, said bicomponent elastomericextruded netting comprising extruded strands consisting essentially of arelatively inelastic resin component and transverse extruded strandsconsisting essentially of a relatively elastic resin component, whereinthe elastic strands are of a styrenic block copolymer composition, andwherein the copolymer composition is a blend of resins.
 11. The nettingof claim 10 wherein the elastic resin further includes a processing aidresin selected from the group consisting of isotatic polypropylene,polyethylene, amorphous polypropylene, polybutylene, ethylene/vinylacetate copolymer, ethylene/ethyl acrylate copolymer, ethylene/methylacrylate copolymer, ethylene/methyl acetate copolymer, polystyrene andmixtures thereof.
 12. The netting of claim 11 wherein the elastic resinincludes about 5-30 parts of the processing aid resin.
 13. The nettingof claim 12 wherein the parts are about
 25. 14. The netting of claim 11wherein the elastic resin includes about 5-30 parts of polystyrene. 15.The netting of claim 11 wherein the elastic resin includes amount of aslip agent.
 16. A bicomponent elastomeric extruded netting havingunidirectional elasticity, said bicomponent elastomeric extruded nettingcomprising extruded strands consisting essentially of a relatively of arelatively inelastic resin component and transverse extruded strandsconsisting essentially of a relatively elastic resin component, whereinthe elastic strands are of a styrenic block copolymer composition, andwherein the elastic resin is a blend of SBS and SIS.
 17. A bicomponentelastomeric extruded netting having unidirectional elasticity, saidbicomponent elastomeric extruded netting comprising extruded strandsconsisting essentially of a relatively inelastic resin component andtransverse extruded strands consisting essentially of a relativelyelastic resin component, and wherein the inelastic strands are apolyolefin and the elastic strands are of a styrenic block copolymercomposition.
 18. A bicomponent elastomeric extruded netting havingunidirectional elasticity, said bicomponent elastomeric extruded nettingcomprising extruded strands consisting essentially of a relativelyinelastic resin component and transverse extruded strands consistingessentially of a relatively elastic resin component, and wherein thestrands of the elastic resin extend in the machine direction and thestrands of the inelastic resin extend in the transverse direction andwherein the inelastic resin is a polyolefin.
 19. A bicomponentelastomeric extruded netting having unidirectional elasticity, saidbicomponent elastomeric extruded netting comprising extruded strandsconsisting essentially of a relatively inelastic resin component andtransverse extruded strands consisting essentially of a relativelyelastic resin component, and wherein the strands of the elastic resinextend in the machine direction and the strands of the inelastic resinextend in the transverse direction and wherein the elastic resin is astyrene-isoprene-styrene resin.
 20. A bicomponent elastomeric extrudednetting having unidirectional elasticity, said bicomponent elastomericextruded netting comprising extruded consisting essentially of arelatively inelastic resin component and transverse extruded strandsconsisting essentially of a relatively elastic resin component, andwherein the strands of the elastic resin extend in the machine directionand the strands of the inelastic resin extend in the transversedirection and wherein the elastic resin is a blend of SBS and SIS.
 21. Abicomponent elastomeric extruded netting having unidirectionalelasticity, said bicomponent elastomeric extruded netting comprising afirst set of extruded strands extending in a first direction and asecond set of extruded strands extending in the opposite transversedirection, one of said strand sets comprising a polypropylene resin andthe other said strand set comprising a styrenic block copolymer resincomposition.
 22. The netting of claim 21 wherein the polypropylene resinstrands extend in the machine direction (MD).
 23. The netting of claim21 wherein the polypropylene resin strands extend in the transversedirection (TD).
 24. The netting of claim 21 wherein the elastic resinblend is comprised of a blend of SIS and SBS.
 25. The netting of claim21 wherein the elastic resin comprises about of 50-70 parts SIS andabout 30-50 parts SBS.
 26. The netting of claim 24 wherein the elasticresin further includes a processing aid resin selected from the groupconsisting of isotatic polypropylene, polyethylene, amorphouspolypropylene, polybutylene, ethylene/vinyl acetate copolymer,ethylene/ethyl acrylate copolymer, ethylene/methyl acrylate copolymer,ethylene/methyl acetate copolymer, polystyrene and mixtures thereof. 27.The netting of claim 26 wherein the elastic resin includes about 5-30parts of the processing aid resin.
 28. The netting of claim 27 whereinthe parts are about
 25. 29. The netting of claim 26 wherein the elasticresin includes about 5-30 parts of polystyrene.
 30. The netting of claim26 wherein the elastic resin includes an amount of a slip agent.
 31. Abicomponent elastomeric extruded netting having unidirectionalelasticity, said bicomponent elastomeric extruded netting comprisingextruded sods consisting essentially of a relatively inelastic resincomponent and transverse extruded strands consisting essentially of arelatively elastic resin component, and wherein the strands of theelastic resin extend in the transverse direction and the strands of theinelastic resin extend in the machine direction and wherein theinelastic resin is a polyolefin.
 32. A bicomponent elastomeric extrudednetting having unidirectional elasticity, said bicomponent elastomericextruded netting comprising exturded strands consisting essentially of arelatively inelastic resin component and transverse extruded strandsconsisting essentially of a relatively elastic resin component, andwherein the strands of the elastic resin extend in the transversedirection and the strands of the inelastic resin extend in the machinedirection and wherein the elastic resin is a styrene-isoprene-styreneresin.
 33. A bicomponent elastomeric extruded netting havingunidirectional elasticity, said bicomponent elastomeric extruded nettingcomprising extruded strands consisting essentially of a relativelyinelastic resin component and transverse extruded strands consistingessentially of a relatively elastic resin component, and wherein thestrands of the elastic resin extend in the transverse direction and thestrands of the inelastic resin extend in the machine direction andwherein the elastic resin is a blend of SBS and SIS.